The term interleukin-1 (IL-1) refers to two different polypeptides (IL-1.alpha. and IL-1.beta.). These two polypeptides possess a wide variety of both immunologic and nonimmunologic activities. IL-1.alpha. and IL-1.beta. are distinct gene products. However, these two polypeptides recognize the same receptor and exhibit the same biological properties. IL-1 is produced in response to a variety of conditions including inflammatory agents, toxins, infection and clotting components. The primary amino acid sequence of human IL-1.alpha. and IL-1.beta. have been reported (Auron et al., Proc. Natl. Acad. Sci. USA, 81, 7907 (1984); and March et al., Nature 315, 641 (1985), respectively). Furthermore, the entire human gene for each form of IL-1 has been cloned and sequenced (Clark et al., Nucleic Acids Res. 14, 7897 (1986); Furutani et al. Nucleic Acids Res. 14, 3167 (1986)).
IL-1 is a small protein of molecular weight about 17.5 kilodaltons, which induces sleep and systemic acute-phase responses including fever, increased hepatic acute-phase protein synthesis, neutrophilia, hypozincemia, hypoferremia and increased levels of hormones when injected into experimental animals. Although IL-1.alpha. and IL-1.beta. have been shown to have distinct primary amino acid sequences (only about 26% amino acid sequence homology), these two polypeptides have been shown to be structurally related by molecular modeling, receptor recognition and crystallographic analysis.
The three dimensional structure of IL-1.beta. has 12 .beta. strands which form a complex of hydrogen bonds as shown by analysis of the tertiary structure of crystallized human IL-1.beta. and computerized molecular modeling. The basic structure is similar to a tetrahedron with an interior filled by hydrophobic side chains. Therefore, the interior of IL-1.beta. is strongly hydrophobic with no charged amino acids.
IL-1.beta. is the more prominent of the two known gene products for IL-1, as evidenced by the greater amount of IL-1.beta. found in culture supernatants and various human body fluids. Furthermore, the amount of IL-1.beta. mRNA found in activated cells is usually about 10 to 50 times greater than the amount of IL-1.alpha. found in these same cells. IL-1.beta. is more readily secreted from activated cells, whereas IL-1.alpha. remains cell-associated.
IL-1.beta. was originally cloned from human blood monocytes, and has subsequently been cloned in cows, rabbits, rats and mice. IL-1.alpha. was originally cloned from the mouse macrophage cell line P388D, and has subsequently been cloned in humans, rabbits and rats.
Several peptides which exhibit some of the same biological properties as IL-1 have been either synthesized (Antoni et al., J. Immunol. 137, 3201 (1986)) or produced by recombinants DNA methods (Rosenwasser et al., Proc. Natl. Acad. Sci. USA 83, 5243 (1986)). However, the specific activities of these peptides are low, and the peptides do no block the receptor binding of mature IL-1. Conventional theories suggest that both the N-terminal and C-terminal amino acids of IL-1 are involved in its receptor binding (Dinarello, Advances in Immunology 44, 153 (1989)).
The histidine residue at position 147 has been substituted by site-specific mutation with a resulting loss of biological activity and receptor binding (MacDonald et al., FEBS Lett. 209, 295 (1986)). However, this histidine residue is located on the surface of the IL-1.beta. molecule.
Other mutations of IL-1.beta. N-terminal amino acids have also resulted in altered biological activity and receptor binding (Horuk et al., J. Biol. Chem. 262, 16275 (1987)). These mutations also suggest that the N-terminal amino acids of IL-1.beta. play an important role by direct interaction with receptor-binding domains.
However, the IL-1.beta. mutants produced to date have not been found to be significantly effective in minimizing, or more importantly, antagonizing the biological activities of IL-1. Such an antagonist of IL-1 would be particularly useful in the treatment of patients with bacterial infection, injury or chronic inflammatory disease.